Apparatus and method for cutting holes in roofing sheet material

ABSTRACT

Apparatus for punching holes in sheet material is provided. At least one cutting knife is mounted for rotation about a first axis. A punching surface of the knife includes end edges that protrude further from the axis than the side edges of the punching surface to permit the end edges to penetrate the sheet material before the side edges sever the sheet material. A cylindrical roll having a groove extending about its circumference is mounted for rotation about a second axis that is parallel to said first axis. The groove forms a pair of continuous cutting edges positioned in cooperative shearing relationship with the side edges of the punching surface of the knife. The new cutting method performed by the apparatus comprises first penetrating the sheet material with the end edges of the punching surface of the knife to form end cut lines which are longitudinally spaced in the sheet material, and then shearing the sheet material along a pair of side cut lines with each side cut line connecting a pair of laterally aligned ends of the end cut lines.

United States Patent [191 Hibbing et a1.

[ APPARATUS AND METHOD FOR CUTTING HOLES IN ROOFING SHEET MATERIAL [75]inventors: Edwin Ernst Hibbing, Castle Rock,

Colo.; Frank Preisier, South Bound Brook, NJ.

[73] Assignee: Johns Manville Corporation,

Greenwood Village, C010.

22 Filed: Sept. 7, 1972 211 App]. No.: 287,117

[52] US. Cl 83/345, 83/664, 83/670 [51] Int. CI 323d 25/12, B26d 1/56[58] Field of Search 83/332, 345, 678, 660, 83/669, 670, 664

[56] References Cited UNITED STATES PATENTS 1,670,317 5/1928 Seymour83/332 3,052,146 9/1962 Glendening 83/660 FOREIGN PATENTS ORAPPLICATIONS 823,694 12/1951 Germany 83/345 710,630 6/1965 Canada 83/332ZE "Q1.

Primary Examiner- Willie G. Abercrornbie It Hi iorne y, Agent, 0r FirmRobert Mt Krone; Stephen C. Shear [5 7] ABSTRACT Apparatus for punchingholes in sheet material is provided. At least one cutting knife ismounted for rotation about a first axis. A punching surface of the knifeincludes end edges that protrude further from the axis than the sideedges of the punching surface to permit the end edges to penetrate thesheet material before the side edges sever the sheet material. Acylindrical roll having a groove extending about its circumference ismounted for rotation about a second axis that is parallel to said firstaxis. The groove forms a pair of continuous cutting edges positioned incooperative shearing relationship with the side edges of the punchingsurface of the knife. The new cutting method performed by the apparatuscomprises first penetrating the sheet material with the end edges of thepunching surface of the knife to form end cut lines which arelongitudinally spaced in the sheet material, and then shearing the sheetmaterial along a pair of side cut lines with each side out lineconnecting a pair of laterally aligned ends of the end cut lines.

8 Claims, 12 Drawing Figures PATENTEDJUN 4 m4 SHEET 1 [If 6 PNENTEU JUNi9 SHEEY 3 M 6 mamm 4 19m .130977 l I i II 2 li II I 0,1,; 1} g H (I) ILO I I q- 5! l l 2% 1 qv M r| ll q BACKGROUND OF THE INVENTION Field ofthe Invention This invention relates to apparatus for cutting sheetmaterial, and more particularly, to apparatus for cutting a plurality ofdistinct holes in roofing material either before or after saturation ofthe material with asphalt or the like.

It is presently the practice to provide perforations in roofing sheetmaterial so that air is not trapped by the roofing material as it isinstalled or as is is formed into rolls for shipping or storing. Presentmethods for perforating webs of roofing material utilize a needle rolland an opposed grooved in wire brush roll. The insertion of the needlesinto the roofing creates perforations, but no roofing material isremoved by the needles and, as a result, the holes in the roofingmaterial have a tendency to close up as the material is wound intorolls.

Because the needles do not remove any roofing material but merely pokethrough the material, the fibers of the material tend to return to theiroriginal position when the roofing is placed into rolls or is otherwisecompressed. This, of course, closes up the holes so that the desiredescape or air does not occur. As a result, undesirable air pockets arefrequently formed beneath the roofing sheet material as it is rolled oras it is being installed.

OBJECTS OF THE INVENTION It is, therefore, an object of the presentinvention to provide an apparatus and method for forming a plurality ofpermanent and distinct holes in roofing or other sheet material byactually removing small amounts of material.

Another object of the invention is to provide a holecutting apparatusthat is durable and easy to maintain.

SUMMARY OF THE INVENTION To achieve these and other objects, the presentinvention provides apparatus for cutting holes in sheet materialcomprising knife means mounted for rotation about a first axis. Apunching surface is provided on the knife means that has the shape ofthe desired hole. The punching surface of the knife means includes endedges that protrude further from the axis than the adjacent portion ofthe side edges of the punching surface to permit the end edges topenetrate the sheet material before the portions of the side edgesadjacent the end edges sever the sheet material. A cylindrical rollhaving a groove extending about its circumference is mounted forrotation about a second axis that is parallel to the first axis. Thegroove forms a pair of continuous cutting edges positioned incooperative shearing relationship with the side edges of the punchingsurface of the knife for shearing the sheet material. The knife meansand the grooved roller thus form a plurality of distinct holes in thesheet material as the material is fed between the knife means and thegrooved cylindrical roll.

In a preferred embodiment, the knife means comprises a shaft mounted forrotation about the first axis and a plurality of knife-holding collars.The collars are concentrically mounted on the shaft for axial movementrelative to the shaft. A plurality of cutting knives are mounted on theknife-holding collars. Holding means, such as a key and set screws areprovided for fixing the rotational and lateral position of theknifeholding collars with respect to the shaft. This segmented rollarrangement, with the collars being axially movable along the shaft,insures that an individual knife can be easily removed from the knifemeans and replaced, if the knife becomes dull or is broken in use.

It is desirable for ease of removal of the knife and particularly thepunching surface from the perforated sheet material that the rearsurface of the knife extend from the back end edge of the punchingsurface towards the cylindrical surface of the knife-holding collar onwhich it is attached in the general direction the knife is rotatingduring the cutting operation. Specifically, the rear surface of theknife is desirably planar, and the plane of this surface intersects thecylindrical surface of the knife-holding collar on which the knife isattached at an angle of from 50-90 with respect to a plane tangent tothe line of intersection of the plane of the knife rear surface and thecylindrical surface of the knife-holding collar.

The invention also provides a method of cutting holes in roofing sheetmaterial comprising the steps of continuously feeding a web of sheetmaterial in a given longitudinal direction; severing the moving sheetmaterial along a pair of laterally-spaced longitudinallyextending lines.Each of the longitudinally-extending shear lines connects a pair oflaterally aligned ends of the laterally extending lines so that atwo-dimensional shape is severed from the sheet of material every time asevering and subsequentshearing operation is performed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate examples of perferred embodimentsof the invention and, together with the description, serve to explainthe principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevation view of anembodiment of the apparatus of this invention.

FIG. 2 is a perspective view of cutting and calendering sections of theapparatus of FIG. 1.

FIG. 3 is a perspective view of a knife constructed in accordance with apreferred embodiment of this invention.

FIG. 4 is an end view of the knife of FIG. 3.

FIG. 5 is an elevation view of a knife-holding collar with a singleknife mounted thereon.

FIG. 6 is an end elevation view of the knife-holding collar and theknife of FIG. 5.

FIG. '7' is an elevation view of a spacer collar.

FIG. 8 is an end elevation view of the spacer collar of FIG. 7.

FIG. 9 is a sectional view of the knife means and grooved cylindricalroll of FIG. 2 and shows the relationship of these cutting elements tosheet material being cut.

FIG. if) is a plan view of sheet material illustrating the rectangularperforations formed by the preferred embodiment of the knife means asillustrated in FlGS. 3-5.

FIG. ll is an end elevation view of one of the roll sections that formthe grooved roll illustrated in FIG. 2; and

FIG. 12 illustrates another embodiment of the knife means of thisinvention. I

DESCRlPTlION OF THE PREFERRED EMBODIMENT With reference now to thedrawings, wherein like reference characters designate like orcorresponding parts throughout the several views, there is shown in FIG.1 means for saturating roofing sheet material with asphalt or the like.As here embodied, the saturating means includes one or more conventionalsaturators provided with a roller l2 for guiding the roofing sheetmaterial 14 toward first drive means generally 16. Drive means 16 areconventional and, as illustrated, include drive rollers 18 and 20 forremoving sheet material 14 from saturators l6 and for directing thesheet material into cutting section 22 and into calendering section 24of the apparatus. The structural details of the cutting and calenderingsections are illustrated in more detail in FIGS. 29.

Calendering section 24 follows cutting sections 22 and is preferablycomprised of two or more rolls 26 that may be heated. Springs 28 and 29or other conventional means may be used for varying the pressure appliedto sheet material 114 as it passes through the cutting and calenderingsections, respectively. The cutting section and the calendering sectionalso may each have conventional air lift cylinders (not shown) for easeof threading the sheet material through the cutting and calenderingsections. The cutting and calendering sections are preferably mounted ona self-standing table 30.

Second drive means generally 32 of conventional construction andincluding rollers 34 cause sheet material M to move first throughcutting section 22 and then through calendering section 24. As hereembodied, conveyor means are also provided for receiving the sheetmaterial from second drive means 32 and preferably for forming sheetmaterial 14 into a plurality of overlapping loops. The conveying meansmay include a conventional looper conveyor 33 upon which the loops areformed and retainer surface 39 cooperating with the conveyor to generatethe loops.

In accordance with the apparatus of the invention, knife means aremounted for rotation about a first axis. The knife means include apunching surface having end edges that protrude further from the axisthan the side edges of the punching surface to permit the end edges topenetrate the sheet material before the side edges contact the sheetmaterial. As here embodied, and as shown in FIG. 2, the cutting sectionpreferably includes a plurality of cutting knives 44 (illustrated indetail in FIGS. 35) mounted on a plurality of knife-holding collars 40for rotation about a first axis defined by the axis of a shaft 42. Asdescribed in more detail below, the end edges of the punching surface ofknives 44 protrude further from the axis of shaft 42 than the side edgesof the punching surface.

In accordance with the invention, a cylindrical roll having a grooveextending about its circumference is mounted for rotation about a secondaxis that is parallel to said first axis. The groove forms a pair ofcontinuous cutting edges positioned in cooperative shearing relationshipwith the side edges of the punching surface of the knife for shearingthe sheet material. As here embodied, a grooved cylindrical rollgenerally 45 includes a second shaft 46 mounted for rotation about itsown axis, and aligned parallel to shaft 42. A plurality of roll sections48 are fixedly mounted on second shaft 46 for rotation therewith asillustrated in H6. 2.

Each roll section 48 is precisely undercut at one end to form a groovewith the adjoining end of the adjacent roll section. Thus, the undercutsform a plurality of grooves having edges 50, as illustrated in FIG. 9,that cooperate with one or more knives 44 for shearing sheet material 14and for forming a plurality of distinct holes in the sheet material asthe material passes between cylindrical roll 45 and cutting knives 44.As best illustrated in FIG. 9, each roll section 48 includes acylindrical member 52 that is undercut at one end to form a cylindricalprojection 54 of smaller diameter that extends axially from one end ofcylindrical member 52. With reference to FIG. 11, a bore 56 and keyway57 extend axially through each roll section 48 for enabling each rollsection to be mounted on second shaft 46 as shown in FlG. 9. The rollsections are fixed on shaft 46 by a key 59, and set screws 61 thatextend through openings 71.

The presently preferred construction of the knife means includes ashaft, knife-holding collars mounted on the shaft, cutting knivesmounted on these collars, and holding means for fixing the rotationaland lateral position of the knife-holding collars with respect to theshaft, and will now be described in detail. With reference to FIG. 12,the holding means includes a plurality of spacer collars 58 that aremounted on shaft 42 with a pair of axially spaced spacer collars 58positioned between each pair of knife-holding collars 40. The spacingbetween the spacer collars permits axial movement of the spacer collarsto permit access to remove the cutting knives from the knife-holdingcollars.

Each knife-holding collar 40, as illustrated in FIGS. 5 and 6, includesan outer cylindrical surface60 and two faces 62 which extend inperpendicular relationship with respect to outer surface 60 and withrespect to the axis of the cylindrical surface. An alternate arrangementof knife-holding collars 40 and spacer collars 58 is illustrated in FIG.2, in which knives 44 are attached on only one face of eachknife-holding collar 40.

As here embodied, the knife means also includes fastening means forattaching a plurality of knives 44 to each collar 40. The fasteningmeans include a plurality of threaded holes 64 formed in each of thefaces 62 (illustrated in FIGS. 5 and 6) for receiving Allen screws 65 orother fastening means so that knives 44 can be secured to collars 40.Each collar 40 includes a centrally-located bore 66 for mounting thecollar on shaft 42. A keyway 67 and a pair of drilled and tappedopenings 69 are provided in each collar 46 for the insertion of a key(not shown) and a pair of set screws (not shown),

- respectively, to fox the collar in place on shaft 42.

Spacer collars 58 are constructed as shown in FlGS. 7 and 8. Each of thespacer collars defined an outer cylindrical surface 68 of the samediameter as surface 60 of collars 40. A centrally-located bore '76 forreceiving shaft 42 extends axially of cylindrical surface 68. One

face of each collar 58 is recessed, and includes a ringshaped centerarea 72 and an outer shoulder 80 that defines an annular ring.

Each spacer collar 53 also includes a keyway 8H and a twoorthogonally-positioned screw-receiving threaded apertures 78 thatextend radially inwardly from cylindrical surface 6% towards bore 76.The apertures enable the insertion of a key (not shown) and set screws(not shown) or other fixing means to hold the spacer collars on firstshaft 42.

When knife-holding collars 4t) and spacer collars 58 are mounted onshaft 42, as illustrated in FIGS. 2 and 9, two spacer collars 53 arepositioned between each pair of knife-holding collars 40. Each spacercollar 58 is provided with an indented ring-shaped area 72 so that thescrews 65 or other fastening means that hold knives 44 onto collars 40can extend into the indented face of collars 58 (see H6. 9). A pair ofspaced spacer collars 58 are used between each knife-holding collar 40to permit axial movement of the spacer collars and to enable thereplacement of a worn or broken knife.

In assembling cutting section 22 of the apparatus, knives 44 are mountedonto knife-holding collars 40 by Allen screws 65. The number of knivesmounted onto each collar is determined by the number of holes that areto be cut into the sheet material per longitudinal foot of material. Ifa large number of holes per unit length of sheet material are to be cut,more knives must be mounted on each collar 40 than ifa smaller number ofholes per unit length of sheet material are to be cut. Collars 40 andpairs of spacer collars 58 are then alternately positioned on shaft 42with the exposed side face of each knife 44 jammed into tight abuttingrelationship with shoulder 80 of a collar 58. Spacer collars 58 areaffixed to shaft 42 by a key (not shown) and set screws (not shown).Knife-holding collars 40, and therefore knives 44 mounted thereon, arealso held in both lateral and rotational alignment with shaft 42 by akey (not shown) and set screws (not'shown) thatextend along theapertures illustrated in FIGS. 5 and 6.-

As best illustrated in FIG. 9, roll sections 48 and I shearing edges 50are precisely laterally positioned on shaft 46 to form grooves 82 forreceiving the knives, with edges 50 positioned to cooperate with theknives to shear spaced longitudinal lines of short length on the roofingsheet material 14 passing between the knife means and grooved roll 45.It should be understood, of course, that instead of providing aplurality of roll sections 48, a single roll with a plurality ofsharp-edged grooves formed therein could be used.

It is an important feature of the present invention that the knife meansprovide a punching surface in which the end edges of the surfaceprotrude further from the axis of revolution of the knife means than theside edges of the punching surface so that the end edges penetrate thesheet material before the side edges sever the material. This punchingsurface design, in combination with the grooved roller described above,insures a sharp cutting action and the severance of small areas of thesheet material from the web. The cutting action produced by thecombination minimizes the tendency to merely displace or disturb fibers,as opposed to cutting them, even when the web of material is being fedat a high linear rate of speed.

A presently preferred design for knives 44 is illus trated in FIGS. 3and 4. Each knife includes a shank 84. A forward front surface 92extends rearwardly from the forward edge 88 of shank 84 with respect tothe direction of rotation of the knife on the apparatus.

in preferred embodiments, and as illustrated in FIG. 3, a cutting tip 94of tungsten carbide or other hard material is affixed to shank 84, whichcan be of mild steel, by a weld or other fastening means. The selectionof other materials of construction for the shank and tip of the knife iswithin the skill of the art. For example, knife 44 may comprise a singlepiece of steel, if the life of the cutting edge is not a criteria ofprime importance.

As illustrated in FIG. 3, a punching surface 96 is provided that has theapproximate shape and area that is desired for the perforation to beformed in sheet material 14. The punching surface is defined by aforward end edge tea, a rear end edge 104, and a pair of arcuate sideedges m5.

Shank 84 includes circular apertures 106 for enabling the knife to befastened to knife-holding collars 40. In the illustrated embodiments,and as shown in FIG. 5, the axes of the apertures in shank 84 arealigned with the axes of a pair of threaded holes 64 that are radiallyspaced along a radius line H07 on knife-holding collar 40.

When a knife 44 is attached to a collar 40, as illustrated in FIG. 5,leading end edge i102 and trailing end edge 104 each protrude furtherfrom the axis of the shaft on which the collar 40 is mounted than theportions of the side edges I05 of the punching surface 96 that areadjacent the respective end edges. Thus, punching surface 96 extendstowards the cylindrical surface 60 of the knife-holding collar 40 onwhich knife 44 is attached in the direction the knife is rotating duringcutting operations, to permit easy withdrawal of knife 44 from thematerial being perforated.

The plane of rear surface desirably intersects the cylindrical surface60 of l knife-holding collar 40 on which knife 44 is attached at anangle of from 50-90 with respect to a plane E22 tangent to the line ofintersection of the plane of rear surface 120 and the cylindricalsurface 60 of knife-holding collar 40. The plane of front surface 92 ofknife 44 is preferably aligned approximately parallel to rear surface120.

In operation of the apparatus illustrated in FIG. 1, sheet material l4passes through saturators 10 in a conventional manner. It should beunderstood, however, that the apparatus is equally effective in actingupon sheet material before or after saturation.

The sheet material is then drawn over roller 12, for example, by firstdrive means 16, and passes over drive rollers 18 and 2G to be fed intocutting section 22 of the apparatus. The material then passes between(a) the segmented roll sections 48 (FIGS. 2 and 9). As material 14 movesahead, shafts 42 and 46 are preferably driven to cause knives 44 torotate about the axis of first shaft 42 and to cause shearing edges 50to rotate about the axis of second shaft 46 in cooperative shearingrelationship with the knives for cutting a plurality of distinct holesin the sheet material as it passes between knives 44 and shearing edgesSt).

The construction of knives 4 permits distinct holes to be cut into sheetmaterial l4. As each knife rotates about shaft 42, forward cutting edgeM32 and rear cutting edge MM!- initially penetrate down through thesheet material. The knife continues to rotate about shaft 42 until sideedges W5 shear the material in cooperation with edges 50. As the knifecontinues to rotate, punching surface 96 protrudes through thehorizontal plane of the sheet material and punches out the previouslysevered piece N8 of material as illustrated in FIG. 9, so that adistinct hole or slot is produced.

A plurality of knives Ml can be mounted circumferentially around eachindividual collar 40 depending upon the number of holes desired per unitlength of material. in addition, the number of knife-holding collars 40and the number of rolls 43 defining shearing edges 50 can be readilyadjusted as determined by the width of the sheet material.

Because the pieces tilt cut from the sheet material may have a tendencyto collect within groove 532 (FIG. 9), doctor blades Hi3 (FlG. B.) maybe positioned to remove the severed pieces from grooves 82 as roll sections 48 rotate about shaft as.

Sheet material M now having a plurality of holes ll2 cut therein (asillustrated in H0. lid) passes from cutting section 22 into calenderingsection 241 and between calendering rolls 26. The calendering sectionmay be made up of two rolls, as illustrated, or more than two rolls maybe used. The calendering rolls may be heated to enhance the Calenderingaction.

Calendering rolls 26 flatten the fibrous material in sheet M, andparticularly in the areas immediately adjacent to the holes formed bythe knives so that the material can be wound into compact rolls to savestorage and shipping space, The Calendering rolls also assist inwithdrawing the sheet material from the cutting section and preventsheet 14 from binding on knives 44 as the sheet material is withdrawnfrom the cutting section.

The flattened sheet material l4, still having a plurality ofdistinctholes therein, is then withdrawn from calendering section 24 of theapparatus by second drive means 32. The sheet material is then fed to aconventional looper section including conveyor 38 and retainer surface39 where the sheet material is formed into a plurality of overlappingloops in a conventional manner.

This invention thus provides a unique apparatus for cutting permanentand distinct holes into sheet mate rial by rotating a plurality ofknives about a first axis, rotating a plurality of shearing edges abouta second axis parallel with the first axis, and by moving the sheetmaterial between the knives and the shearing edges whereby a pluralityof distinct holes are cut into the sheet material.

The invention in its broader aspects is not limited to the specificdetails shown and described, and departures may be made from suchdetails without departing from the principles of the invention andwithout sacrificing its chief advantages.

What is claimed is:

1. Apparatus for forming holes in sheet material, comprising:

a. at least one cutting knife mounted for rotation along and extendingout from a circular path about a first axis, said knife including apunching surface having a perimeter that has the approximate desiredshape of the holes, said punching surface of said knife including aleading end cutting edge and a trailing end cutting edge that protrudefurther from said axis than the adjacent portions of the side edges ofthe cutting surface to permit said end edges to penetrate the sheetmaterial before said side edges sever the sheet material;

b. said knife further including a planer rear surface which extends fromthe trailing end edge of said cutting surface towards said circular pathin the direction said knife is rotating during cutting operations, topermit easy withdrawal of said knife from the material being cut, saidplaner rear surface intersecting said circular path at an angle of from5090 with respect to a plane tangent to the line of intersection of theplane of said rear surface and said circular path; and

c. a cylindrical roll having a groove extending about its circumference,said roll being mounted for rotation about a second axis that isparallel to said first axis, with the groove forming a pair ofcontinuous cutting edges positioned in cooperative shearing relationshipwith the side edges of the punching surface of said knife for shearingsaid sheet material and thus forming a plurality of distinct holes inthe sheet material as the material is fed between the knife-and thegrooved cylindrical roll.

2. The apparatus of claim 1 including a shaft mounted for rotation aboutthe first axis; a plurality of knife-holding collars, said collars beingconcentrically mounted on said shaft for movement along said shaft, theouter cross-sectional surface of said collars lying on said circularpath; a plurality of said cutting knives mounted on said knife-holdingcollars; and holding means for fixing the lateral and rotationalposition of said collars with respect to said shaft.

3. The apparatus of claim 2 in which the holding means comprise aplurality of spacer collars concentrically mounted on said shaft, saidspacer collars mounted for movement along said shaft and positioned witha knife-holding collar between each of said spacer collars; and a setscrew fixing the lateral and rotational position of each of said spacercollars with respect to said shaft.

4. The apparatus of claim 2 in which the side edges of said punchingsurface are each arcuate.

5. The apparatus of claim 3 in which side edges of said punching surfaceare each arcuate.

6. The apparatus of claim 1 wherein said trailing end edge protrudesfurther from said axis than said leading end edge.

7. An apparatus for forming holes in sheet material, comprising:

a. at least one cutting knife mounted for rotation along and extendingout from a circular path about an axis, said knife including a punchingsurface having a perimeter that has the approximate desired shape of theholes, said punching surface of said knife including a leading endcutting edge and a trailing end cutting edge that protrude further fromsaid axis than the adjacent portions of the side edges of the cuttingsurface to permit said end edges to penetrate the sheet material beforesaid side edges sever the sheet material;

b. said knife further including a planer rear surface which extends fromthe trailing end edge of said cutting surface towards said circular pathin the direction said knife is rotating during cutting operahaving aperimeter that has the approximate desired shape of the holes, saidpunching surface of said knife including a leading end edge and atrailing end edge that protrude further from said axis than the adjacentportions of the side edges of the punching surface to permit said endedges to penetrate the sheet material before said side edges, saidtrailing edge protruding further from said axis than said leading edge;and

b. means cooperating with said knife for shearing said sheet material.

1. Apparatus for forming holes in sheet material, comprising: a. atleast one cutting knife mounted for rotation along and extending outfrom a circular path about a first axis, said knife including a punchingsurface having a perimeter that has the approximate desired shape of theholes, said punching surface of said knife including a leading endcutting edge and a trailing end cutting edge that protrude further fromsaid axis than the adjacent portions of the side edges of the cuttingsurface to permit said end edges to penetrate the sheet material beforesaid side edges sever the sheet material; b. said knife furtherincluding a planer rear surface which extends from the trailing end edgeof said cutting surface towards said circular path in the direction saidknife is rotating during cutting operations, to permit easy withdrawalof said knife from the material being cut, said planer rear surfaceintersecting said circular path at an angle of from 50*-90* with respectto a plane tangent to the line of intersection of the plane of said rearsurface and said circular path; and c. a cylindrical roll having agroove extending about its circumference, said roll being mounted forrotation about a second axis that is parallel to said first axis, withthe groove forming a pair of continuous cutting edges positioned incooperative shearing relationship with the side edges of the punchingsurface of said knife for shearing said sheet material and thus forminga plurality of distinct holes in the sheet material as the material isfed between the knife and the grooved cylindrical roll.
 2. The apparatusof claim 1 including a shaft mounted for rotation about the first axis;a plurality of knife-holding collars, said collars being concentricallymounted on said shaft for movement along said shaft, the outercross-sectional surface of said collars lying on said circular path; aplurality of said cutting knives mounted on said knife-holding collars;and holding means for fixing the lateral and rotational position of saidcollars with respect to said shaft.
 3. The apparatus of claim 2 in whichthe holding means comprise a plurality of spacer collars concentricallymounted on said shaft, said spacer collars mounted for movement alongsaid shaft and positioned with a knife-holding collar between each ofsaid spacer collars; and a set screw fixing the lateral and rotationalposition of each of said spacer collars with respect to said shaft. 4.The apparatus of claim 2 in which the side edges of said punchingsurface are each arcuate.
 5. The apparatus of claim 3 in which sideedges of said punching surface are each arcuate.
 6. The apparatus ofclaim 1 wherein said trailing end edge protrudes further from said axisthan said leading end edge.
 7. An apparatus for forming holes in sheetmaterial, comprising: a. at least one cutting knife mounted for rotationalong and extending out from a circular path about an axis, said knifeincluding a punching surface having a perimeter that has the approximatedesired shape of the holes, said punching surface of said knifeincluding a leading end cutting edge and a trailing end cutting edgethat protrude further from said axis than the adjacent portions of theside edges of the cutting surface to permit said end edges to penetratethe sheet material before said side edges sever the sheet material; b.said knife further including a planer rear surface which extends fromthe trailing end edge of said cutting surface towards said circular pathin the direction said knife is rotating during cutting operations, topermit easy withdrawal of said knife from the material being cut, saidplaner rear surface intersecting said circular path at an angle of50*-90* with respect to a plane tangent to the line of intersection ofthe plane of said rear surface and said circular path; and c. meanscooperating with said knife for shearing said sheet material.
 8. Anapparatus for forming holes in sheet material, comprising: a. at leastone cutting knife mounted for rotation along and extending out from acircular path about an axis, said knife including a punching surfacehaving a perimeter that has the approximate desired shape of the holes,said punching surface of said knife including a leading end edge and atrailing end edge that protrude further from said axis than the adjacentportions of the side edges of the punching surface to permit said endedges to penetrate the sheet material before said side edges, saidtrailing edge protruding further from said axis than said leading edge;and b. means cooperating with said knife for shearing said sheetmaterial.